The plant cell nucleus is constantly alert and highly sensitive to repetitive local mechanical stimulations

When mechanical stimulation is applied to a plant cell, the nucleus usually shows oriented movement to the site of stimulation (as a defensive response). Former researchers have revealed that applying mechanical pressure to plant tissues could line up cell division plane. A proposal, therefore, was put forward that cells inside plant tissue could receive mechanical signals from their growing neighbors to adjust their nuclear position and thus regulate the orientation of their dividing plane in order to form characteristic morphology of plant organs. To explore nuclear capacity and sensitivity to rapidly changing signals, multiple mechanical stimulations were applied to the same plant cell at intervals, either locally or at distance. The results revealed that the nucleus was highly sensitive to mechanical stimulations. It responded quickly to both local and distant stimulation by showing oriented movement toward the stimulation site. The nucleus was able to respond immediately to a second stimulation (no time lag) by starting up a second oriented movement toward the new signal; the completion of nuclear oriented movement to a first site of stimulation was not necessary for startup of a subsequent movement track to a second stimulation site, regardless of whether the second stimulation was applied ahead of or behind the moving nucleus. The nucleus responded to a second stimulation without loss of velocity, whether or not it was in a resting or moving state. This novel finding favors the proposal that growing tissues adjust the location of nuclei in cells by varying mechanical pressures; they thus control cell division according to a plan whereby organs and their constituent tissues develop in an orderly, specified manner. It appears that the enhanced sensitivity of plant cells to mechanical pressure is necessary not only in response to the external environment, but also to the developmental microenvironment inside the tissues.